These systems have a particular mode of communication, the so-called half-duplex mode, which has long since disappeared from public systems (public switched telephone network, or public radiocommunications systems such as GSM). In the half-duplex mode, a mobile station can send or receive, but cannot perform both these operations at once (i.e., push-to-talk functions or emit/receive function). Moreover, a single mobile station must be authorized to send at a given instant, the data flow sent by this mobile station being retransmitted to the mobile station or stations participating in the communication (also called a call), that is to the mobile station concerned when dealing with an individual communication or to all the mobile stations participating in the communication when dealing with a group communication.
A particular network equipment, called the central equipment in what follows, performs arbitration in case of conflict between requests for the right to send reaching it from different mobile stations through corresponding base stations. This arbitration is based on a level of priority and/or on the identity of the mobile stations. The central equipment notifies the various mobile stations of the result of this arbitration, that is it indicates the mobile station to which the right to send has been granted. It must also, as the case may be, warn the other mobile stations of the end of the alternation (i.e., press-to-talk time period, or emit/receive time period) in progress, that is of the cessation of sending by the mobile station which had previously obtained the right to send, so that these other mobile stations can in their turn request the right to send. It must also, as the case may be, allow the preemption of alternation by a mobile station having a higher priority than that which enjoys the right to send for the alternation in progress.
The major development of packet switching transport networks in non connected mode makes it possible to envisage the management of a communication between at least two base stations of a radiocommunications system that are regarded as end equipments of such a network.
In particular, use may be made of the mechanisms of the multimedia conferences defined within the framework of internet protocols, that is protocols for networks operating according to the IP protocol (J. Postel, “Internet Protocol”, RFC 791, IETF, September 1981) which has been standardized by the IETF (“Internet Engineering Task Force”) organization in the above RFC (Request For Comments). These multimedia conferences are based on the implementation of a multimedia video conferencing equipment or MCU (standing for “Multimedia Conferencing Unit”), and offer an advantageous support for producing numerous types of telephony and videophony services for example. However, the principal internet protocols have been designed for conventional multimedia applications and do not take account of the specific features of certain applications of professional radiocommunications networks, and in particular the management of alternation for communications in half-duplex mode.
It is therefore seen to be desirable to adapt the protocols implemented in packet switching transport networks in non connected mode, for allowing the management of alternation for communications in half-duplex mode, be they individual communications or group communications.